feat(preview): fanned deck of cards on multi-select

When `selection.ids.size >= 2`, the inline preview swaps the single-
photo view for a SelectionDeck: each selected thumbnail renders as
an absolutely-positioned card with a translate + rotate computed
from its index in the deck, so the spread reads as a fan. CSS
transition-transform handles the reflow as the deck grows or
shrinks; `in:fly` lands new cards from above, `out:scale` shrinks
removals into the stack. Hash resolution walks the existing
TanStack caches (per-photo + photos-infinite envelope) so the deck
is side-effect-free — no fetches just to render thumbs.

Drop the now-redundant Maximize hover affordance on PhotoTile and
the `onOpenPreview` plumbing through PhotoGrid / +page.svelte:
single-click already places a tile into the inline preview pane,
so the dedicated "open preview" button no longer has a job.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/lib/components/timeline/PhotoGrid.svelte

@@ -81,13 +81,6 @@
 		setFocused(uid);
 		setAnchor(uid);
 	}
-
-	function onOpenPreview(uid: string) {
-		selection.ids.clear();
-		selection.ids.add(uid);
-		setFocused(uid);
-		setAnchor(uid);
-	}
 </script>
 
 <div data-photo-grid class="grid gap-2" style="grid-template-columns: {tracks};">
@@ -99,7 +92,6 @@
 				selected={sel}
 				onClick={(e) => onClick(e, photo.UID)}
 				onDblclick={(e) => onDblclick(e, photo.UID)}
-				onOpenPreview={() => onOpenPreview(photo.UID)}
 			/>
 		</div>
 	{/each}